An unusual case of leiomyosarcoma (LMS) of the maxillary gingiva is discussed here; this case presents a unique pattern of tumor growth and a long period between initial discovery and correct pathological diagnosis. The tumor was incompletely resected twice by a private dentist over a period of 3 years, with a clinical diagnosis of epulis, no pathological examination was conducted during this period. When it was finally removed, the tumor was very large (50 x 35 x 12 mm in size and 18 g in weight), consisting of an easily hemorrhagic mass originating in the gingival mucosa with the growth pattern of a polyp. Following an extensive surgical excision and a unilateral radical neck dissection, the patient has been free of LMS for 8 years. In light of this case, we strongly emphasize the importance of conducting a pathological examination, even though clinical examination seems to indicate a diagnosis of epulis or granulation. In this way, the presence of LMS can be ascertained in a timely manner with better prognosis for treatment and recovery.